Golden Cinnamon Bundt Cake

For the Vanilla Custard

• 1½ cups milk
• 7 tablespoons granulated sugar divided
• 4 large egg yolks
• 3½ tablespoons cornstarch
• 1 tablespoon unsalted butter
• 1½ teaspoons pure vanilla extract

For the Cake

• 3 cups cake flour
• 3 tablespoons ground cinnamon
• 2 teaspoons baking powder
• 1 teaspoon kosher salt
• 1 cup unsalted butter room temperature (2 sticks)
• 1 cup granulated sugar
• 5 large eggs room temperature
• ¾ cup milk room temperature
• ½ cup sour cream room temperature

For the Topping

• ¼ cup brown sugar
• ¼ cup granulated sugar
• 1 tablespoon ground cinnamon
• 3 tablespoons unsalted butter melted

For the Vanilla Custard

• Whisk 1½ cups of milk and half of the granulated sugar together in a large saucepan set over medium-high heat. Bring the mixture to a gentle boil, then reduce the heat to low and simmer for 1 minute, allowing the sugar to fully dissolve and infuse the milk.
  1½ cups milk, 7 tablespoons granulated sugar (divided)
  
• While the milk is gently simmering, whisk 4 large egg yolks in a separate medium-sized bowl until they are smooth and slightly pale. In a small, dry bowl, combine the remaining granulated sugar (3½ tablespoons) and 3½ tablespoons of cornstarch, mixing them thoroughly to prevent lumps.
  4 large egg yolks, 3½ tablespoons cornstarch
  
• Swiftly whisk the cornstarch-sugar mixture into the egg yolks. It’s crucial to do this just before combining with the milk, as the cornstarch can cause the egg yolks to solidify if left to stand too long. Continue whisking until the mixture is completely smooth and free of any visible lumps.
  
• To temper the egg yolks, gradually add ¾ cup of the warm milk mixture from the saucepan to the egg yolk mixture, whisking constantly and vigorously. This prevents the eggs from scrambling. Once combined into a smooth, tempered mixture, carefully pour it back into the remaining milk in the saucepan.
  
• Continue to heat the mixture over low heat, whisking constantly for another 2-3 minutes. Keep whisking until the custard thickens noticeably and coats the back of a spoon, or reaches an internal temperature of 185°F (if using an instant-read thermometer). The mixture will become thick and luscious. If you notice any small clumps forming, whisk vigorously against the sides of the pan to break them up and ensure a silky-smooth custard.
• Remove the saucepan from the heat. Stir in 1 tablespoon of unsalted butter and 1½ teaspoons of pure vanilla extract until fully incorporated, adding richness and depth of flavor. Transfer the hot custard to a clean bowl and immediately cover the surface directly with plastic wrap to prevent a “skin” from forming as it cools. Allow the custard to cool completely to room temperature.
  1 tablespoon unsalted butter, 1½ teaspoons pure vanilla extract
  
• Once the custard has reached room temperature, spoon it carefully into a piping bag (or a sturdy zip-top bag with one corner snipped off). Set it aside, ready for filling the cake.

For the Cake

• Preheat your oven to 350°F (175°C). Prepare your 10-cup Bundt pan: if using a metal pan, generously grease every curve and crevice with vegetable shortening (like Crisco), then dust thoroughly with flour, tapping out any excess. If you’re using a silicone Bundt pan, no greasing or flouring is necessary. Set the prepared pan aside.
• In a medium bowl, thoroughly whisk together 3 cups of cake flour, 3 tablespoons of ground cinnamon, 2 teaspoons of baking powder, and 1 teaspoon of kosher salt. Ensuring these dry ingredients are well combined prevents pockets of unmixed leavening agents in your final cake. Set this mixture aside.
  3 cups cake flour, 3 tablespoons ground cinnamon, 2 teaspoons baking powder, 1 teaspoon kosher salt
  
• In the bowl of a stand mixer fitted with a paddle attachment, combine 1 cup of room temperature unsalted butter and 1 cup of granulated sugar. Beat on medium-high speed for approximately 2 minutes, or until the mixture becomes notably light, fluffy, and pale in color. This creaming process incorporates air, which is essential for a tender cake crumb.
  1 cup unsalted butter, 1 cup granulated sugar
  
• Add 5 large, room temperature eggs to the butter and sugar mixture, one at a time, beating well after each addition until fully incorporated. This ensures a smooth, emulsified batter. Then, gently whisk in ¾ cup of room temperature milk and ½ cup of room temperature sour cream until just combined. Using room temperature dairy prevents the batter from seizing and ensures a uniform texture.
  5 large eggs, ¾ cup milk, ½ cup sour cream
  
• With the mixer on low speed, gradually add the dry ingredients to the wet ingredients in 2-3 additions. Mix only until the ingredients are just combined and no streaks of flour remain. Be careful not to overmix, as this can develop the gluten in the flour too much, resulting in a dense, chewy, and less tender cake.
  
• Carefully pour approximately ¾ of the prepared cake batter into your greased and floured Bundt pan, spreading it evenly across the bottom and up the sides.
  
• Snip a small corner off your piping bag (or zip-top bag) containing the cooled custard. Pipe the creamy custard in a continuous circle directly into the center of the batter in the Bundt pan. This ensures the custard stays centered during baking. Then, carefully spoon the remaining cake batter over the custard layer, gently spreading it to cover the filling completely.
  
• Bake the cake for 75-80 minutes. To check for doneness, insert a clean toothpick into the sides of the cake (avoiding the custard-filled center, as the custard will wet the toothpick). If the toothpick comes out clean or with a few moist crumbs, the cake is fully baked.
  
• Allow the baked cake to cool in the Bundt pan for 30-45 minutes on a wire rack. This cooling period is crucial for the cake to set and firm up, making it easier to unmold without breakage. Before it cools completely (while still slightly warm), carefully invert the pan to remove the cake onto a cooling rack. Let it continue to cool on the rack.
• While the cake is cooling, prepare the irresistible churro topping. In a small bowl, whisk together ¼ cup of brown sugar, ¼ cup of granulated sugar, and 1 tablespoon of ground cinnamon until thoroughly combined.
  ¼ cup brown sugar, ¼ cup granulated sugar, 1 tablespoon ground cinnamon
  
• Once the cake is still slightly warm (this helps the butter and sugar adhere better), brush a small section of the cake with 3 tablespoons of melted unsalted butter. Immediately sprinkle or gently press the cinnamon-sugar mixture onto the buttered section. Continue this process, working in small sections, until the entire cake is generously coated with the sweet, spiced topping. Slice and serve your magnificent churro bundt cake!
  3 tablespoons unsalted butter
  

• **Pan Preparation is Key:** For metal bundt pans, thoroughly coat every intricate detail of the pan – first with vegetable shortening (like Crisco) followed by a generous dusting of flour. This crucial step creates a non-stick barrier, ensuring your beautiful cake releases seamlessly from the pan without sticking or tearing.
• **Custard Consistency:** While an instant-read thermometer (aim for 185°F) is helpful for precision when making the vanilla custard, it’s equally important to observe its consistency. The custard is done when it thickens to a spoonable texture that holds its shape, similar to a thick pudding.
• **Testing for Doneness:** To accurately check if your churro bundt cake is fully baked, insert a toothpick into the sides of the cake. It’s essential to avoid poking directly into the custard-filled center, as the moist custard will always make the toothpick appear wet, giving a false reading. A clean toothpick from the cake portion indicates readiness.
• **Room Temperature Ingredients:** Always ensure your butter, eggs, milk, and sour cream are at room temperature before you begin mixing the cake batter. This allows them to emulsify properly, creating a smooth, cohesive batter and ultimately a more tender and evenly baked cake.

Storage: Store any leftover custard-filled churro bundt cake in an airtight container in the refrigerator for up to 4 days. Due to its creamy custard filling, refrigeration is recommended to maintain freshness and food safety. We do not recommend freezing this cake, as the custard can separate or become soggy upon thawing, compromising the texture and quality of this delicious treat.